The invention relates in general to casting of vehicle wheels and in particular to an improved wheel mold for casting vehicle wheels which has a retractable ball cap.
Vehicle wheels have a circular wheel disc attached to an annular wheel rim. The wheel disc includes a central wheel hub having a pilot hole and plurality of wheel mounting holes formed therethrough. A plurality of equally circumferentially spaced spokes typically support the wheel hub within the wheel rim. The wheel rim is adapted to support a pneumatic tire.
In the past, vehicle wheels typically have been formed entirely from steel. However, wheels formed from light weight metals, such as aluminum, magnesium and titanium or alloys thereof, are becoming increasingly popular. In addition to weighing less than conventional all-steel wheels, such light weight wheels can be manufactured having a pleasing esthetic shape. Weight savings also can be achieved by attaching a wheel disc formed from a light weight metal alloy to a steel wheel rim.
Light weight wheels are typically formed by forging or casting operations. During a casting operation, molten metal is poured into a cavity formed in a multi-piece wheel mold. After the metal cools sufficiently to solidify, the mold is opened and a rough wheel casting is removed. The wheel casting is then machined to a final shape. Machining can include turning the outside and inside surfaces of the wheel rim, facing the inboard and outboard wheel disc surfaces and drilling the center pilot hole and the mounting holes through the wheel hub.
Referring now to the drawings, there is illustrated in FIG. 1 a typical prior art multi-piece wheel mold 10. The mold includes a base member 11 which supports movable left and right side members 13 and 14, respectively. The side members 13 and 14 are moved in a horizontal direction by a conventional mechanism (not shown). A movable cup shaped top core 15 is received by the side members 13 and 14. A ball riser cup 16 having an inverted cup shape is attached to the center of the top core 15. The side members and top core 15 cooperate with the base member 11 to define a mold cavity 20. The mold cavity 20 includes a disc cavity 21 and an annular rim cavity 22. An annular rim riser 23 is formed at the upper end of the rim cavity 22. Similarly, the ball riser cap 16 defines a ball riser 24 in the center of the disc cavity. 21.
The right side member 14 has a gate 30 formed therein. The gate 30 includes an inlet chamber 31 which receives a charge of molten metal. The inlet chamber 31 communicates with an intermediate chamber 32. An axial slot 33 formed in an inside wall of the intermediate chamber 32 communicates with the rim cavity 22.
To cast a wheel, the mold 10 is closed and molten metal poured into the gate 30. The metal flows by gravity into the rim and disc cavities 22 and 21. The molten metal also fills the rim and ball riser cavities 23 and 24, respectively. As the molten metal within the rim and disc cavities 22 and 21 cools and shrinks, gravity urges additional molten metal from the rim and ball riser cavities 23 and 24 and into the rim and disc cavities 22 and 21. This additional metal fills any voids that are formed by shrinkage of the molten metal during cooling and solidification. The metal remaining in the riser cavities 23 and 24 cools to form a center ball riser and an annular rim riser on the casting. Similarly, any metal remaining in the mold gate forms a sprue on the casting. The casting risers and sprue are typically sawed from the casting during the machining operation.
This invention relates to an improved wheel mold for casting vehicle wheels which has a retractable ball cap.
Prior art wheel molds are charged with molten metal through a side gate. This causes an uneven thermal distribution of heat within the mold. Accordingly, it would be desirable to provide an alternate mold structure for charging the mold which would provide a more uniform thermal distribution of heat within the mold.
The present invention contemplates a mold for casting a component for a vehicle wheel which includes a base member and a movable top core. The top core cooperates with the base member to define a mold cavity. The mold also includes a combined central riser and gate extending axially from the center of the top core. The combined central riser and gate allows gravity charging the center of the mold cavity with molten metal. This results in a uniform thermal distribution of heat within the mold.
It is further contemplated that the combined central riser and gate can include a plurality of movable ball riser cap segments mounted upon the center of the top core. The riser cap segments cooperate to define the gate for charging the mold cavity with molten metal. In the preferred embodiment, a porous filter is disposed in the base of the gate.
Also in the preferred embodiment, each of the riser cap segments has a bore formed therein and each of the bores receives a guide pin. The guide pins are mounted upon the upper surface of the top core base. The guide pins form an angle with the top core and extend in an outward radial direction such that the riser cap segments are movable along the guide pins in an outward radial direction and in an axial direction away from the base of the top core when the riser cap segments are retracted.
Alternately, a plurality of ramps can be formed upon the upper surface of the top core base. The riser cap segments are supported by the ramps and movable along the ramps in an outward radial direction and in an axial direction away from the base of the top core. Additionally, either the ramps can have a guide rail formed thereon with the guide rails being received by corresponding grooves formed in the riser cap segments, or the riser cap segments can have a guide rail formed thereon with the guide rails being received by corresponding grooves formed in the ramps.
The mold can be used to cast a full face wheel disc or a wheel spider. The mold can further include a plurality of movable side members, the mold being used to cast one piece wheels.
The invention further contemplates a method for casting a vehicle wheel component which includes providing a multiple piece mold having a base member and a top core which cooperate to define a mold cavity. The top core carries a plurality of movable ball riser cap segments mounted upon the center thereof. The riser cap segments define a gate for the mold cavity. The mold is closed first and then the ball riser cap segments are closed to form a gate for charging the mold cavity. A charge of molten metal is poured through the gate formed by the riser cap segments and into the mold cavity. The metal is allowed to cool sufficiently to solidify. The ball riser cap segments are retracted first and then the mold is opened. Finally, the casting is removed from the mold. It is further contemplated that the method includes inserting a porous filter between the ball riser cap segments before closing the segments, whereby the charge of molten metal flows through the filter.
Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings.